The coupled climate models used to hindcast past and project future climate in the IPCC’s 2007 report AR4 were not initialized so that they could reproduce the multidecadal variations that exist in the global temperature record. This has been known for years. For those who weren’t aware of it, refer to Nature’s ClimateFeedback:Predictions of climate post, written by Kevin Trenberth.

The question this post asks is, should the IPCC’s coupled climate models be initialized so that they reproduce the multidecadal variability that exists in the instrument-based global temperature records of the past 100 years and project those multidecadal variations into the future.

And for the future, the [IPCC] draft gives even less succour to those seeking here a new mandate for urgent action on greenhouse gas emissions, declaring: “Uncertainty in the sign of projected changes in climate extremes over the coming two to three decades is relatively large because climate change signals are expected to be relatively small compared to natural climate variability”.

That’s IPCC speak, and it really doesn’t say they’re expecting global surface temperatures to flatten for the next two or three decades. And we have already found that at least one of the climate models submitted to the CMIP5 archive for inclusion in the IPCC’s AR5 does not reproduce a multidecadal temperature signal. In other words, that model shows no skill at matching the multidecadal temperature variations of the 20th Century. So the question still stands:

Should IPCC climate models be Initialized so that they replicate the multidecadal variability of the instrument temperature record during past 100 years and project those multidecadal variations into the future?

In the post An Initial Look At The Hindcasts Of The NCAR CCSM4 Coupled Climate Model, after illustrating that the NCAR CCSM4 (from the CMIP5 Archive, being used for the upcoming IPCC AR5) does not reproduce the multidecadal variations of the instrument temperature record of the 20th Century, I included the following discussion under the heading of NOTE ON MULTIDECADAL VARIABILITY OF THE MODELS :

…And when the models don’t resemble the global temperature observations, inasmuch as the models do not have the multidecadal variations of the instrument temperature record, the layman becomes wary. They casually research and discover that natural multidecadal variations have stopped the global warming in the past for 30 years, and they believe it can happen again. Also, the layman can see very clearly that the models have latched onto a portion of the natural warming trends, and that the models have projected upwards from there, continuing the naturally higher multidecadal trend, without considering the potential for a future flattening for two or three or four decades. In short, to the layman, the models appear bogus.

To help clarify those statements and to present them using Sea Surface Temperatures, the source of the multidecadal variability, I’ve prepared Figure 1. It compares observations to climate model outputs for the period of 1910 to year-to-date 2011. The Global Sea Surface Temperature anomaly dataset is HADISST. The model output is the model mean for the hindcasts and projections of the coupled climate models of Sea Surface Temperature anomalies that were prepared for the Fourth Assessment Report (AR4) from the Intergovernmental Panel on Climate Change (IPCC) published in 2007. As shown, the period of 1975 to 2000 is really the only multidecadal period when the models come close to matching the observed data. The two datasets diverge before and after that period.

Figure 1

Refer to Animation 1 for a further clarification. (It’s a 4-frame gif animation, with 15 seconds between frames.) It compares the linear trends of the Global Sea Surface Temperature anomaly observations to the model mean, same two datasets, for the periods of 1910 to 1945, 1945 to 1975, and 1975 to 2000. Sure does look like the models were programmed to latch onto that 1975 to 2000 portion of the data, which is an upward swing in the natural multidecadal variations.

Animation 1

A NOTE ABOUT BASE YEARS: Before somebody asks, I used the period of 1910 to 1940 as base years for anomalies. This period was chosen for an animation that I removed and posted separately. The base years make sense for the graphs included in that animation. But I used the same base years for the graphs that remain in this post, which is why all of the data has been shifted up from where you would normally expect to see it.

Figure 2 includes the linear trends of the Global Sea Surface Temperature observations from 1910 to 2010 and from to 1975 to 2000 and includes the trend for the model mean of the IPCC AR4 projection from 2000 to 2099. The data for the IPCC AR4 hindcast from 1910 to 2000 is also illustrated. The three trends are presented to show this disparity between them. The long-term (100 year) trend in the observations is only 0.054 deg C/decade. And keeping in mind that the trends for the models and observations were basically identical for the period of 1975 to 2000 (and approximately the same as the early warming period of 1910 to 1945), the high-end (short-term) trends for a warming period during those 100 years of observations is about twice the long-term trend or approximately 0.11 deg C per decade. And then there’s the model forecast from 2000 to 2099. Its trend appears to go off at a tangent, skyrocketing at a pace that’s almost twice as high as the high-end short-term trend from the observations. The model trend is at 0.2 deg C per decade. I said in the earlier post, “the layman can see very clearly that the models have latched onto a portion of the natural warming trends, and that the models have projected upwards from there, continuing the naturally higher multidecadal trend, without considering the potential for a future flattening for two or three or four decades.” The models not only continued that trend, they increased it substantially, and they’ve clearly overlooked the fact that there is a multidecadal component to the instrument temperature record for Sea Surface Temperatures. The IPCC projection looks bogus to anyone who takes the time to plot it. It really does.

Figure 2

CLOSING

The climate models used by the IPCC appear to be missing a number of components that produce the natural multidecadal signal that exists in the instrument-based Sea Surface Temperature record. And if these multidecadal components continue to exist over the next century at similar frequencies and magnitudes, future Sea Surface Temperature observations could fall well short of those projected by the models.

SOURCES

Both the HADISST Sea Surface Temperature data and the IPCC AR4 Hindcast/Projection (TOS) data used in this post are available through the KNMI Climate Explorer. The HADISST data is found at the Monthly observations webpage, and the model data is found at the Monthly CMIP3+ scenario runs webpage. I converted the monthly data to annual averages for this post to simplify the graphs and discussions. And again, the period of 1910 to 1940 was used as the base years for the anomalies.

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About Bob Tisdale

Research interest: the long-term aftereffects of El Niño and La Nina events on global sea surface temperature and ocean heat content. Author of the ebook Who Turned on the Heat? and regular contributor at WattsUpWithThat.

To me, temperatures should have been the last thing scientists should be concerned about.
By the planets standards…it is what it is.

In say that, there are far more interesting thing to be looking at and studying.
But too much focus on temperature to the exclusion of all other areas really massively screwed up science. Mind you, our past theories did not help. They too also muddied the water of knowledge.

@ Joe Lalonde
The “Temperature of Earth” was something I could never get my head sorted out about. Now “Global Ice Volume” that’s different, I think I could get my head adjusted to that. Problem is we don’t have much historic data that’s reliable about ‘Ice” and a lot of people think they can see something “Global” in all the local temps accumulated over the past few hundred years.

It really does make sense to take 20th Century temps as the base for future climate projections, but ICE is something you can definitely get your teeth into.😉

I could never understand how looking at temperatures for an Ice Age when it is massive precipitation based. So the equator can be hotter than hell and the rest of the planet is under tons of snow and yet temperatures could show only slight cooling.
Now that we have a drop of 5mm of sea level, you can expect massive amounts of precipitation.

I can’t find the link to the HADISST data you cited. I have cross-referenced the global figures with HadSST2 and I find that your published data are very far from what HadSST2 suggests.

For instance, the 30 year (360 month) trend in HadSST2 is 0.14 C/decade (exactly what the model projection suggests), and not 0.08 C/decade as stated. The 17 year (204 month) trend in HadSST2 is 0.09C/decade, and not 0.02 C/decade as stated.

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NOTES ON GRAPHS

If you use one of my graphs or other illustrations, please provide a link to the post where it was found.

Also, please advise me via a comment if an illustration does not appear in a post. The image hosting site loses them occasionally. I have the illustrations on file and should be able to replace/repair them. Thanks.